Thin film formed by inductively coupled plasma

ABSTRACT

Silicon nitride is formed on a supporting substrate by chemical vapor deposition using an antenna outside a vacuum reaction chamber to apply RF power to form an inductively coupled plasma from a reactant gas.

This is a divisional of application Ser. No. 08/820,293 filed Mar. 18,1997.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to an inductively coupled plasma chemical vapordeposition(ICP CVD) technology, and more particularly, to amorphoussilicon, micro crystalline silicon, thin film silicon nitride and thinfilm amorphous silicon transistors fabricated by the utilizationthereof.

2. Related Art

Generally, thin amorphous silicon, micro crystalline silicon andamorphous silicon film have been widely used in semiconductor and liquidcrystal devices. In addition, thin amorphous silicon filmtransistors(a-Si TFT) have been widely used as driving elements of pixelelectrodes in liquid crystal displays. In particular, a hydrogenizedamorphous silicon transistor(a-Si:H TFT) is widely used for itssuperiority in the areas of yield and utilization in large area displaydevices.

Plasma enhanced chemical vapor deposition(PECVD) is currently used tomanufacture thin amorphous silicon film, thin micro crystalline siliconfilm, thin silicon nitride film and thin amorphous silicon filmtransistors. But this type of vapor deposition due to its low plasmadensity of 10¹⁰ cm⁻³ has low vapor deposition rate and requires high gaspressure. This results in fabrication problems due to polymer formation.In addition, due to the electrode substances existing in the dischargearea of the reaction chamber, thin film product is contaminated thusdegrading thin film quality.

As available methods of plasma production, inductively coupled plasmadeposition and capacitively coupled plasma deposition are provided.Inductively coupled plasma deposition is shown to be more efficient thancapacitively coupled plasma deposition. Using inductively coupled plasmadeposition, it is possible to produce plasma having a higher densitysuch as 10¹¹-10¹² cm⁻³, and for discharging to take place under lowpressures such as 0.1-20 mTorr. (Refer to P. N Wainman et al., J. Vac.Sci. Technol., Al3(5), 2464, 1995.)

In the laid-open publication of Japanese patent application (No.95-60704), there is disclosed, an inductively coupled plasma chemicalvapor deposition apparatus. The above patent application, however, doesnot present the manufacturing method for amorphous silicon film,microcrystalline silicon film, thin silicon nitride film and thinamorphous silicon film transistors possessing superior electrical andoptical matter properties. In addition, in the above disclosedapparatus, dielectric shield is made of material containing oxygen, suchas quartz, and during deposition, the generated plasma causes etching ofthe dielectric shield, resulting in the dissociation of oxygen and otherimpurities from the dielectric shield which adversely effects thin filmquality. Furthermore, in the above mentioned inductively coupled plasmachemical vapor deposition apparatus, gas injection holes which form aportion of gas supply unit are not located at a central region of thereaction chamber but to the side of the chamber. What results is theirregular distribution of supplied reactant gas, making difficult, theproduction of thin films having a large surface area. Namely, the abovementioned apparatus has a shortcoming a uniform and high density plasmawithin the reaction chamber is not produced.

According the ICP CVD method of the present invention, a uniformamorphous silicon is provided having superior electrical and otherphysical properties in areas such as photo sensitivity, electricconductivity, and optical band gap. In addition, uniform film siliconnitride with superior physical properties in areas such as electricconductivity, break down voltage, current density is provided. Thinuniform film silicon with fine crystalline grain size is also provided.Additionally, a thin film transistor having a uniform amorphous siliconfilm is provided with superior electrical properties in areas such aselectric field effect mobility, and threshold voltage. Thus a TFT-LCD ofquality can obtained according the present invention.

SUMMARY OF THE INVENTION

The first object of the present invention is to provide an inductivelycoupled plasma chemical vapor deposition method capable of manufacturingan uniform amorphous silicon film having superior properties in areas ofphoto sensitivity, electric conductivity, activation energy, and opticalband gap.

The second object of the present invention is to provide an inductivelycoupled plasma chemical vapor deposition method capable of manufacturingan uniform silicon nitride film having superior thin film properties inareas of break down voltage, and current density.

The third object of the present invention is to provide an inductivelycoupled plasma chemical vapor deposition method capable of producing athin silicon film having fine and uniform crystalline grains.

The fourth object of the present invention is to provide an inductivelycoupled plasma chemical vapor deposition method capable of producingthin film transistor containing uniform amorphous film silicon, havingsuperior electrical properties in areas such as electric field effectmobility.

In order to accomplish the above objects of the present invention, thereis provided an inductively coupled plasma chemical vapor depositionmethod for depositing a selected thin film on a substrate frominductively coupled plasma, the method including the steps of: providinga vacuum reaction chamber including an interior bounded, in part by adielectric shield, the dielectric shield having an amorphous siliconlayer on its interior surface, an antenna arranged outside thedeposition chamber adjacent to the dielectric shield, where RF power isapplied; placing the substrate on a stage within the vacuum reactionchamber; exhausting the vacuum reaction chamber to provide a vacuumstate; introducing a reactant gas to the vacuum reaction chamber at apredetermined pressure; and applying RF power to the antenna, wherebyinductively coupled plasma for deposition of a thin film from thereactant gas is formed within the vacuum reaction chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention may be betterunderstood with reference to the following detailed description,appended claims, and attached drawings wherein:

FIG. 1 is a descriptive view of the inductively coupled plasma CVDapparatus in accordance with an embodiment of the present invention;

FIG. 2A is a schematic diagram of the antenna structure used in theinductively coupled plasma CDV of FIG. 1;

FIG. 2B is a schematic diagram of an alternative antenna structure usedin the inductively coupled plasma CDV of FIG. 1;

FIG. 3A is a sectional view of the inverted staggered type thinamorphous silicon film transistor manufactured in accordance with anembodiment of the present invention;

FIG. 3B is a sectional view of the inverted staggered type thinamorphous silicon film transistor manufactured in accordance with analternative embodiment of the present invention.

FIG. 4 is a graph showing FR-IR property of a thin amorphous siliconfilm transistor manufactured in accordance with an embodiment of thepresent invention;

FIG. 5 is a graph showing electrical conductivity of the thin amorphoussilicon film manufactured in accordance with an embodiment of thepresent invention;

FIG. 6 is a graph showing optical band gap of the thin film amorphoussilicon manufactured in accordance with an embodiment of the presentinvention;

FIG. 7 is a graph showing light absorption property of the thinamorphous silicon film manufactured in accordance with an embodiment ofthe present invention;

FIG. 8 is a graph showing electric conductivity property of a n-typethin amorphous silicon film manufactured in accordance an embodiment ofthe present invention;

FIG. 9 is a graph showing degree of crystallization and Ramman peakfull-width at half-maximum(FWHM) of a thin microcrystalline silicon filmmanufactured in accordance with an embodiment of the present invention;

FIG. 10 is a graph showing electrical conductivity property of a n-typethin microcrystalline silicon film manufactured in accordance anembodiment of the present invention;

FIG. 11 is a graph showing Fourier transform infrared (FT-IR) propertyof a thin silicon nitride film manufactured in accordance with anembodiments of the present invention;

FIG. 12 is a graph showing current-voltage property of the thin siliconnitride film manufactured in accordance with an embodiment of thepresent invention;

FIG. 13A is a graph showing output property of the thin amorphoussilicon film transistor manufactured in accordance with the conventionalPECVD method;

FIG. 13B is a graph showing output property of a thin amorphous siliconfilm transistor manufactured by the ICP CVD method in accordance with anembodiment of the present invention;

FIG. 14A is a graph showing drain current-gate voltage property of athin amorphous silicon film transistor manufactured in accordance withthe conventional art;

FIG. 14B is a graph showing drain current-gate voltage property of thethin amorphous silicon film transistor manufactured in accordance withan embodiment of the present invention;

FIG. 15A is a graph showing electric field effect mobility of a thinamorphous silicon film manufactured in accordance with the conventionart; and

FIG. 15B is a graph showing field effect mobility of the thin amorphoussilicon film manufactured in accordance with an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an inductively coupled chemical vapor deposition apparatus10 fabricated according to the present invention. The ICP CVD apparatusincludes a vacuum reaction chamber 11. The vacuum reaction chamber 11includes a cylindrical side plate 12, an upper plate 13, and a bottomplate 14. In order to maintain the vacuum reaction chamber 11 in asealed state, there is provided O-shaped ring(hereinbelow referred to asO-ring) seals 15A and 15B between the cylindrical side plate 12 and theupper plate 13, and between the cylindrical side plate 12 and the bottomplate 13, respectively.

A dielectric shield made of quartz material is formed as the upper plate13. An insulating ceramic material other than quartz, such as Al₂O₃ canalso be applied as the upper plate 13. Al₂O₃ allows the transmittance ofradio frequency power, but blocks out infrared rays.

In order to prevent pollution of the chamber 11 by oxygen or otherimpurities that are dissociated by etching of the dielectric shield 13during vapor deposition process, a silicon layer 16 absent of oxygen isprovided on the inner surface of the dielectric shield 13 of the vacuumreaction chamber 11. The silicon layer 16 absent of oxygen is composedof amorphous silicon, being about 1,000 Å in thickness. Silicon nitrideor silicon carbide may also be used instead of amorphous silicon. Use ofthe silicon layer absent of oxygen is a major feature in the presentinvention.

An antenna 17 is installed on the outer surface of the dielectric shield13. For the antenna 17, it is preferred that a spiral type be provided,which: facilitates application of RF power to a large area; provides asuperior and more uniform distribution of RF power; and is relativelysimple in shape(refer to H. Sugai et al., Jpn. J. Appl. Phys., 33, 2189,1994, & Y. Horiike et al., J. vac. Sci. Technol. A13(3), 801, 1995). Foruse in the current embodiment, either one of the two spiral antennas asshown in FIG. 2A and FIG. 2B is preferably used to obtain a plasmadensity of 10¹¹-10¹² cm⁻³.

As shown FIGS. 2A and 2B, the antenna 17 includes terminals 17 a and 17b where RF power is to applied, and coil part 17 b.

The antenna 17 is also coupled to a matching box 18. The matching box 18is coupled to a RF power source 19.

A stage 20 is installed piercing through the central portion of thebottom plate 14. A work piece to be fabricated, for example, glasssubstrate 21 is mounted on the stage 14. An outlet line 22 forexhausting gases from the vacuum reaction chamber 11 is provided at apredetermined position of the bottom plate 14. The stage 20 iselectrically insulated from the bottom plate 14, and is designed to havecooling and heating capabilities necessary for plasma deposition.

Reactant gases are supplied into the vacuum reaction chamber 11 by oneor more gas supply tubes. The present embodiment shows use of two gassupply tubes 24 and 25. A plurality of gas storage tanks 23 are coupledto the gas supply tubes 24 and 25, in order to supply two or morereactant gases.

The gas supply tubes 24 and 25 includes ring-shaped parts 24A and 25A,which are formed to be positioned at the central portion of the vacuumreaction chamber 11 for a wide and uniform distribution of reactantgases. At predetermined portions along the periphery of respectivering-shaped parts 24A and 25A, there are provided a plurality of nozzles24B and 25B equally spaced apart at constant intervals.

A method for selected thin film vapor deposition by reactant gasinductively coupled plasma is explained hereinbelow.

A work piece to be fabricated, for example, a glass substrate 21 ismounted on the stage 20 inside the chamber 11. The air inside thechamber 11 is exhausted through the outlet line 22 establishing a vacuumhaving a pressure of 10⁻⁶-10⁻⁷ Torr. Electrical current is then appliedand the stage 20, whereby the stage is heated to the temperature of300-500° C.

Reactant gases are supplied to the vacuum reaction chamber 11.Pre-selected reactant gases are supplied from the gas storage tanks 23to the gas supply tubes 24 and 25. Afterwards, the supplied gases in thegas supply tubes 24 and 25 are introduced into the vacuum reactionchamber 11 through the plurality of nozzles 25A and 25B of thering-shaped parts 24A and 24B. The reactant gases are selected fromdielectric, metal and semiconductor composition gases so that thin filmvapor deposition is possible corresponding the selected elements ofeither dielectric substances, metals, or semiconductor substances. Poweris applied to the antenna 17 from the RF source 19 through the matchingbox 18.

Inductively coupled plasma is thus formed inside the above chamber inorder to form a thin film on the substrate 21. The reactant gasessupplied forms an inductively coupled plasma which is of a uniform andhigh density, having a peak ion density of 10¹¹-10¹² cm⁻³.

Hereinbelow, the deposition method of forming various thin filmsaccording to the present invention, are described

1. Vapor Deposition of Thin Amorphous Silicon Film

A substrate is mounted on the stage inside the vacuum reaction chamber.While the substrate is kept in vacuum state, SiH₄ is supplied to thechamber through the gas inlet nozzles of the gas supplying unit. Siliconsource gases other than SiH₄ such as Si₂H₆, SiH₂Cl₂, etc. may also beused. In the present embodiment, the SiH₄ gas has a flow of 0.5 SCCM anda pressure of 70 mTorr. RF power at 40 W is applied to the spiralantenna placed adjacent to the chamber to form inductively coupledplasma. After the substrate temperature reaches 250° C., thin amorphoussilicon film is deposited on the substrate.

2. Vapor Deposition of Thin Film Silicon Nitride

A substrate is mounted on the stage inside the vacuum reaction chamber.While the substrate is kept in vacuum state, SiH₄/NH₃/He is supplied tothe chamber through the gas inlet nozzles of the gas supplying unit. Inthe present embodiment, the SiH₄ gas has a flow of 0.5-2.0 SCCM, NH₃ gashas a flow of 10-60 SCCM, He gas has a flow of 10-100 SCCM. SiH₄/NH₃ hasa flow rate ratio ranging from 1:10 to 1:30. The total gas pressureranges from 500-800 mTorr. RF power at 10-120 W is applied to the spiralantenna placed adjacent to the chamber to form inductively coupledplasma. After the substrate temperature reaches 200-300° C., thin filmsilicon nitride is deposited on the substrate.

3. Vapor Deposition of Thin Film Micro Crystalline

A substrate to be fabricated is mounted on top of the stage inside thevacuum chamber. While the work piece to be fabricated is mounted in thevacuum state, gases of SiH₄/H₂/He are supplied to the chamber throughthe gas inlet nozzles of the gas supply unit. In the above step, the gasflows of SiH₄, H₂, He are 0.5-2 SCCM, 5-100 SCCM, 10-100 SCCMrespectively, the SiH₄/H₂ having a flow rate ratio was 1:10-1:50. Thetotal gas pressure is approximately 200-500 mTorr. RF power of 10-120 Wis applied to the spiral antenna to produce inductively coupled plasmainside the chamber. Substrate temperature is raised to 200-300° C. andthin film is deposited on the substrate to be fabricated.

4. Fabrication of Thin Amorphous Silicon Film Transistors

Thin amorphous silicon film transistors having inverted staggeredstructure as shown in FIG. 3A is explained below.

First, on the insulating substrate 30, metal patterned gate 31 of Cr,Al, etc., is formed.

Afterwards, gate insulating layer 32 made of nitride film is formed onthe entire surface of the above structure. The gate insulating layer 32was 3000 Å in thickness in this particular embodiment. The vapordeposition occurred when the flow of gases of SiH₄, NH₄, He were 0.5SCCM, 25 SCCM, 70 SCCM respectively, and when the substrate temperaturewas 300° C. and the gas pressure was 580 mTorr.

On top of the gate insulating layer 32, hydrogenized amorphoussilicon(a-Si:H) pattern 33 is formed to serve as a channel or activelayer. The condition for amorphous silicon vapor deposition is asfollows: gas flow of SiH₄ of 0.5 SCCM; substrate temperature of 250° C.;RF power of 40 W; gas pressure of 430 mTorr.

Furthermore, on both sides of the hydrogenized amorphous silicon pattern33, heavily doped n-type (n⁺) source/drain regions 34 are formed. Inaddition, the n⁺ source/drain regions 34 form ohmic contact withsource/drain electrodes 35. As n⁺ source/drain regions 34(generallycalled to ohmic contact layer), n⁺ hydrogenized amorphous silicon(n⁺a-Si:H) or n⁺ microcrystalline silicon(μc-Si) can be used, which formohmic contact with source/drain electrodes 35, to enhance ohmicproperty. The vapor deposition condition for the ohmic contact layer isas follows: gas flow of SiH₄ of 0.5 SCCM; gas flux of PH₃ of 0.015 SCCM;gas flow of He of 50 SCCM; substrate temperature of 250° C.; electricalpower of 40 W; gas pressure of 430 mTorr.

An alternative fabricating method for thin amorphous silicon filmtransistor having inverted staggered structure as shown in FIG. 3B isexplained below.

First, gate electrode 31 made of Cr, Al, etc. is formed. Afterwards, ICPCVDs of silicon nitride for the gate insulation layer and hydrogenizedamorphous silicon layer 33 takes place, forming an active layer. In theformation of the ohmic contact, Al/Cr is used in source/drain electrodes35 formation after n⁺ amorphous silicon or the n⁺ microcrystallinesilicon as the ohmic contact layer 36 is formed.

Furthermore, for the above insulating layer 32 staggered structuredSiO₂/SiN or Al₂O₃/SiN may be used instead for mass productionenhancement.

Amorphous silicon is generally used as active layer 33 in a-Si:H TFTs.The properties of this amorphous silicon are determining factors in theproperties of the TFT. Most of the above amorphous silicon today ismanufactured using conventional PECVD apparatus.

Hereinafter, experimental results of electrical and optical propertiesof thin amorphous silicon film, thin silicon nitride film, and thinamorphous silicon film transistors are explained in detail in accordancewith FIG. 4 to FIG. 15B.

FIG. 4 shows the FT-IR(fourier transform infrared) characteristic forthin amorphous silicon film fabricated according to the presentembodiment. Here, infrared region absorption coefficient of the thinamorphous silicon film vapor deposited on the single crystalline siliconwafer is measured with a BOMEN 100 FT-IR spectroscope. The spectrummeasurement results in the infrared ray region show that stretch mode ofthe Si—H bond appears at a wave number of 2,000 cm⁻¹ and bend mode ofthe Si—H bond appears at wave number 610 cm⁻¹. From the above result itbecomes clear that the film formed in the present embodiment a typicalthin amorphous silicon film. Si—H2 bond is not found in the film formedby this embodiment, and hydrogen content calculated from Si—H bond isfound to be 14 at.

FIG. 5 is a graph showing the electrical conductivity of amorphoussilicon film formed in accordance to the present embodiment. Herein, aproduct of Corning 7059 is used as the substrate. On the substrate,there is provided an amorphous silicon film formed by the inductivelycoupled vapor deposition method. On the amorphous silicon film, thereare provided aluminum electrode films formed with a coplanar structureby thermal deposition method. Thereafter, the substrate 21 is mounted onthe stage 20 of the inductively coupled plasma CVD apparatus.Afterwards, conductivity as a function of temperature is measured withKeithley electrometer 617 and Keithley multimeter 197. From themeasurement result, dark conductivity at room temperature andphotoconductivity at a condition of AM-1 are respectively calculated,the former being of 4.3×10⁻¹² Ω⁻¹cm⁻¹ and the latter 1.4×10⁻⁵ Ω⁻¹cm⁻¹.The condition of AM-1 is one where light radiates the specimen at 100mW/cm². In addition, activation energy was measured to be 1.05 eV. Fromthe above results, photosensitivity of the thin amorphous silicon filmvapor deposited in accordance with the present invention is shown to be3×10⁻⁶ indicating that the amorphous material possesses superiorphysical properties.

FIG. 6 is a graph showing optical band gap of thin amorphous siliconfilm formed by inductively coupled plasma CVD apparatus in accordancewith the present invention. Optical absorption coefficient a of thinamorphous silicon film deposited on the glass substrate of Corning 7059is measured with a UV/VIS spectrometer. Optical band gap is obtainedfrom the measured optical coefficient data and optical band gap iscalculated from the following equation:

(αhν)^(½) =B(E−E _(g) ^(opt))

In the above equation, B is a constant indicating the slope of the band,hν is the incident photon energy, α is optical absorption coefficient,and E_(g) ^(opt) is optical band gap.

As shown in FIG. 6, optical band gap is 1.78 eV. From the above result,the thin film formed in the present embodiment is determined to be atypical thin amorphous silicon film.

FIG. 7 is a graph showing light absorption characteristic in thinamorphous silicon film formed by inductively coupled plasma CVDapparatus according to the present invention. Urbach energy, E_(u) isthe slope of band tail in the graph of FIG. 7 showing absorptioncoefficient as a function of light energy at a range of 1.6-1.8 eV. Theenergy is obtained from the following equation:

α=α₀exp(hν/E _(u))

wherein, α is optical absorption coefficient, α₀ is a constant, and hνis a incident photon energy. In addition, density of defect states,N_(d) is obtained from the following equation:

N _(d)=1.9×10¹⁶∫α_(ex)(hν)d(hν)

wherein, α_(ex) has the following relation(refer to Xu. X et al., Jpn.J. Appl. Phys., 26, L1818, 1987):

α_(ex)=α−α0exp(hν/Eu)

Urbach energy, Eu and density of defect states, Nd are calculated fromthe above-mentioned equations, respectively being 58 meV and 7.43×10¹⁵cm⁻³eV⁻¹. The values obtained, indicate that the formed film is typicalthin amorphous silicon film.

FIG. 8 is a graph showing conductivity in n-typed amorphous siliconfilm, the film being formed by inductively coupled plasma chemical vapordeposition apparatus fabricated according to the embodiment of thepresent invention. Herein, the measurement method for thinmicrocrystalline silicon film is also applied to measurement for thinn-typed amorphous silicon film deposited on glass substrate. From themeasurement result, dark conductivity at room temperature and activationenergy are respectively calculated, the former being 7×10⁻³ Ω⁻¹cm⁻¹ andthe latter 0.22 eV. From the above results, the thin amorphous siliconfilm obtained according to the present invention has superior propertiesin regard to doping efficiency.

Next, thin microcrystalline silicon film is described.

FIG. 9 is a graph showing degree of crystallization and full-width athalf maximum(FWHM) which are obtained from Raman scattering of thinmicrocrystalline silicon film, the film being deposited according to theratio of H₂/SiH₄ in inductively coupled plasma CVD apparatus of thepresent invention.

There is provided a specimen wherein thin microcrystalline silicon filmis deposited on a glass substrate of Corning 7059. Degree ofcrystallization and FWHM of microcrystalline silicon film formed, areobtained using Raman spectroscopy(refer to H. Kakinuma et al., Jpn. J.Appl. Phys. 70, 7374, 1991). Grain size of the microcrystalline siliconfilm formed, is 200-400 Å, and degree of crystallization is 70-73% asshown in FIG. 8. In considering that typical microcrystalline siliconfilm has a grain size of 30-200 Å and a degree of crystallizationranging from 2% to 70% (refer to K. Nomoto et al., Jpn. J. Appl. Phys.29, L1372, 1990), the grain size and the degree of crystallizationobtained in the present embodiment indicates that the formedmicrocrystalline silicon film has superior physical properties.

FIG. 10 is a graph showing conductivity in n-typed microcrystallinesilicon film, the film being formed by inductively coupled plasmaapparatus fabricated according to the embodiment of the presentinvention. Herein, a product of Corning 7059 is used as the substrate.On the substrate, there is provided the thin n-doped microcrystallinesilicon film formed from the above method. On the microcrystallinesilicon film, there are provided aluminum electrode films formed in thecoplanar structure by thermal deposition method. Thereafter, thesubstrate is mounted on the stage 20 of the inductively coupled plasmaCVD apparatus in FIG. 1 and held in a fixed position. Afterwards,conductivity as a function of temperature is measured using Keithleyelectrometer 617 and Keithley multimeter 195A. From the measurementresult, dark conductivity at room temperature and activation energy arerespectively calculated, the former being 17 Ω⁻¹cm⁻¹ and the latter 30meV. From the above results, the thin n-doped microcrystalline siliconfilm obtained according to the present invention has superior propertiesin regards to doping efficiency.

Next, thin silicon nitride film is described.

FIG. 11 shows Fourier transform infrared(FT-IR) characteristic of thinsilicon nitride film according to the present invention. Herein,transmittance at infrared ray region is measured for a specimen whereinthin nitride silicon film is deposited on single crystalline siliconsubstrate with high conductivity. A FT-IR spectroscope made by the BOMENcompany is used as the apparatus for measurement. The measured spectrumresult at the infrared ray region shows a stretch mode of N—H bond at awave number of 3,340 cm⁻¹ and a bend mode of N—H bond at wave number1,150 cm⁻¹ appear. In addition, wagging mode of Si—N bond is shown at awave number of 840 cm⁻¹. From the above result, the film formed in thepresent embodiment is determined to be a typical thin silicon nitridefilm.

FIG. 12 is a graph showing current-voltage property of thin siliconnitride film formed in inductively coupled plasma CVD apparatus of thepresent invention.

After a thin silicon nitride film with thickness of approximate 1,000 Åis deposited on p-typed single crystalline silicon substrate having aresistivity of 10-15 Ωcm, an aluminum layer with diameter of 1 mm isformed on the thin silicon nitride film in vacuum by thermal depositionmethod. Through the above processes, a specimen for test ofcurrent-voltage property with MIS structure is fabricated.Current-voltage property of the specimen is measured using Keithleyelectrometer 617. From the measurement, breakdown voltage is 7 MV, andcurrent density is 10⁻¹⁰ A/cm²¹ at 1 MV/cm.

Lastly, thin amorphous silicon film is described.

FIG. 13A is a graph showing an output property of thin filmtransistor(TFT) including an amorphous silicon film fabricated accordingto plasma enhanced chemical vapor deposition(PECVD) method of theconventional art. FIG. 13B is a graph showing drain current as afunction of drain voltage according to gate voltage(Vg), which isaccording to the present invention. Provided TFT has a width(W) of 60 μmand a length of 30 μm.

When gate voltage of 20 V is applied to the gate electrode, draincurrent in TFT fabricated according to the conventional art is saturatedat 1.3 μA, while drain current in TFT fabricated according to thepresent invention is saturated at 2.0 μm, as shown in FIGS. 13A and 13B.From the measurement result, it is determined that TFT according to thepresent invention has a superior ohmic contact layer than that of theTFT fabricated according to the conventional art. In addition, the TFTfabricated according to the present invention has greater rate ofincrease in drain current than that of the TFT fabricated according tothe conventional art as gate voltage increases.

FIG. 14A is a graph showing drain current-voltage characteristic of thinfilm transistor(TFT) including amorphous silicon film fabricatedaccording to PECVD method of the conventional art, the TFT having thestructure of FIG. 3A. FIG. 14B is a graph showing drain current as afunction of gate voltage at a drain voltage(V_(d)) of 5V, according tothe present invention.

As shown in FIGS. 14A and 14B, off current of TFT fabricated accordingto the conventional art approaches a value of 10⁻¹¹ order, while offcurrent in TFT fabricated according to the present invention approachesa value of 10⁻¹² order which is lower than that of the conventional artby 1 order(10⁻¹ A). Not shown in the drawings, it was measured thathydrogenized amorphous TFT(an amorphous silicon containing hydrogenatoms) fabricated using inductively coupled plasma CVD apparatusaccording to the present invention has a subthreshold voltage ofapproximately 0.36 V/dec, and a on/off ratio of more than 10⁶.

FIG. 15A is a graph showing field effect mobility of TFT includingamorphous silicon film fabricated according to the conventional art.FIG. 15B is a graph showing field effect mobility of TFT includingamorphous silicon fabricated according to the present invention.

Field effect mobility, μ_(FE) is calculated from the following equation:

(I _(D))^(½)={μ_(FE)(W/L)C _(i)(V _(G) −V _(TH))V _(D)}^(½)

wherein: threshold voltage as applied in FIGS. 15A and 15B, is 6 V;μ_(FE) in FIG. 15B is 0.80 cm²/Vs; and μ_(FE) in FIG. 15A is 0.60cm²/Vs.

From the results obtained, the thin amorphous silicon film obtainedaccording to the present invention has superior properties than the thinamorphous silicon film obtained according to the conventional art, indoping efficiency.

As described in the present embodiments, inductively coupled plasma CVDapparatus according to the present invention can obtain uniform plasmawith high density in the vacuum reaction chamber, wherein the apparatushas: a silicon layer absent of oxygen, the silicon layer being formed ondielectric shield, ring-shaped parts connected to gas supply means, thegas supply means being established such that it is positioned at thecentral portion of the reaction chamber, and a plurality of gas supplynozzles formed along its periphery at a constant intervals. Thus, thepresent invention can provide a thin amorphous silicon film withsuperior physical properties in areas such as photosensitivity,conductivity, activation energy, and optical band gap with a uniformthickness throughout its surface. In addition, there is also provided athin silicon nitride film with superior physical properties in areassuch as breakdown voltage and current density are superior and thicknessand with a uniform thickness throughout its surface. Moreover, there isprovided a thin microcrystalline silicon film wherein grain size is verysmall and surface thickness is uniform throughout. In addition, thepresent invention provides a thin film transistor including a thinamorphous silicon film with superior electrical properties in areas offield effect mobility and threshold voltage so that it is possible tofabricate a thin film transistor liquid crystal display (TFT-LCD) ofhigh quality.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in a thin film of the presentinvention without departing from the spirit or scope of the invention.Thus, it is intended that the present invention covers the modificationsand variations of this invention provided they come within the scope ofthe appended claims and their equivalents.

What is claimed is:
 1. A thin silicon nitride film formed on asupporting substrate by inductively coupled plasma, wherein said thinsilicon nitride film has a breakdown voltage of 7 MV and has a currentdensity of 10⁻¹⁰ A/cm² at 1 MV/cm.